Force RustRover to semi-work with Rust installations from Nixpkgs#
Works by creating a toolchain in your .idea folder.
Tested with a toolchain from Nixpkgs, see examples/nixpkgs.nix. Probably
also works with fenix, see examples/fenix.nix.
TODO:
- An example of using in Flakes (without relying on
toString ./.being the impure project root)